Wafer level fabrication techniques provide for the efficient and high volume production of optical elements and other components used in optical imaging apparatus. Existing wafer level fabrication techniques for optical elements employ a transparent substrate wafer onto which optical structures, such as lenses, are formed. The transparent substrate wafer provides mechanical rigidity to the optical elements, thereby facilitating downstream handling and processing. Moreover, transparent wafer substrates provide surfaces for the installation of one or more apertures for controlling the transmission of the desired amount of electromagnetic radiation to or from other optical components or sensing components of an optical system.
FIG. 1 illustrates a wafer level optical element employing a substrate. The optical element (100) of FIG. 1 consists of a substrate (102), a first lens structure (104) deposited on a surface of the substrate (102) and a second lens structure (106) deposited on the opposing side of the substrate (102). An aperture (108) for the optical element (100) is additionally formed on a surface of the substrate (102).
The use of transparent substrate wafers, however, does present several disadvantages. One disadvantage is a reduction in modulation transfer function (MTF) values when a transparent substrate is disposed between lens structures. Moreover, substrate wafers can place design and/or mechanical restraints on optical structures deposited on the wafers. Substrate wafers, for example, can restrain the minimum center thickness of the optical element. Also, substrate wafers may behave differently over temperature fluctuations than the lens structures. Furthermore, substrate wafers contribute a significant amount to the cost of producing optical elements.